1. Field of the Invention
This invention relates generally to an electrophotographic copying apparatus and more particularly to an electrophotographic apparatus of the liquid developing and transfer type.
2. Description of the Prior Art
In a conventional electrophotographic copying apparatus, a drum type photosensitive member is rotated and charged and then exposed to a light image to form an electrostatic latent image, and the thus formed latent image is developed and the excess liquid developer on the photosensitive member is removed. Thereafter the developed image is transferred onto a transfer material and the transferred image is fixed.
Various kinds of apparatus have been known for removing the excess liquid developer. Such apparatuses are, for example, corona squeezing types using corona discharge as shown in U.S. Pat. No. 3,722,994, contact roller squeezing types using a roller in press-contact with the photosensitive member, air-knife squeezing types using air directed toward the photosensitive member, blade squeezing types using a blade disposed in the close vicinity of the photosensitive member, and rotating roller squeezing types using a roller disposed and rotating in the close vicinity of the photosensitive member.
However, when the excess liquid developer is removed by the above described apparatuses, except for corona discharge squeezing type, even if the excess liquid developer is removed sufficiently and there is no disturbance of the developed image on the photosensitive member, an insulating carrier liquid still remains among the toner particles forming the liquid developer so that the developed image will be disturbed when the image is transferred, consequently, the transferred image has defects in which, for example, fine lines become blurred, net points become broken, black areas or thick lines are disturbed and transfer is deteriorated, which would result in unclear and non-uniform transferred image.
On the other hand, if the carrier liquid attached among the toner particles of the liquid developer is completely removed, the transfer operation can not be performed smoothly which results in a deteriorated transfer.
Therefore it has been known that for obtaining a good transferred image it is necessary to retain a suitable amount of the liquid developer after the liquid developer has been squeezed.